Slacker seat tube = more of your body weight behind the bottom bracket = less weight on your hands, and = more compatible with a more upright riding position. Steeper seat tube = more body weight forward of the bottom bracket = more weight on your hands and = more compatible with a more bent-over, powerful riding position. It all boils down to, do you want to be better able to sit upright and enjoy the view, or do you want to hammer at high speed?